Implement thread list update feature

lib/main.dart

@@ -93,6 +93,20 @@ class _MyHomePageState extends State<MyHomePage> {
           // Here we take the value from the MyHomePage object that was created by
           // the App.build method, and use it to set our appbar title.
           title: Text(widget.title),
+          actions: [
+            TextButton.icon(
+                onPressed: () {
+                  ScaffoldMessenger.of(context).showSnackBar(
+                    const SnackBar(
+                        content: Text('Обновление списка тредов...')),
+                  );
+                  Provider.of<ThreadListModel>(context, listen: false).update();
+                },
+                label: const Text("Обновить"),
+                style: TextButton.styleFrom(
+                    primary: Theme.of(context).colorScheme.onPrimary),
+                icon: Icon(Icons.sync))
+          ],
         ),
         body: Center(
           child: Container(

lib/thread_list_model.dart

@@ -6,6 +6,8 @@ class ThreadListModel extends ChangeNotifier {
   String currentGroup = "";
   NNTPClient? client;
   Map<String, Map<int, List<ThreadItem>>> threads = {};
+  int _pageNum = -1;
+  List<ThreadItem> _curItems = [];
 
   Future<void> selectNewsgroup(String name) async {
     if (currentGroup == name) return;
@@ -13,27 +15,29 @@ class ThreadListModel extends ChangeNotifier {
     currentGroup = name;
     await client!.selectGroup(name);
     threads.putIfAbsent(name, () => {});
+    _curItems.clear();
+    _pageNum = -1;
 
     notifyListeners();
   }
 
-  Future<List<ThreadItem>> getNewThreads(
-      int perPage, int pageNum, bool clearCache) async {
+  Future<List<ThreadItem>> getNewThreads(bool clearCache) async {
     if (currentGroup == "") return [];
-    List<ThreadItem> items = [];
+
+    _pageNum += 1;
 
     if (clearCache) {
       threads[currentGroup]?.clear();
     }
 
-    if (threads[currentGroup]!.containsKey(pageNum)) {
-      items.addAll(threads[currentGroup]![pageNum]!);
+    if (threads[currentGroup]!.containsKey(_pageNum)) {
+      _curItems.addAll(threads[currentGroup]![_pageNum]!);
     } else {
-      var resp = await client!.getNewThreads(perPage, pageNum);
+      var resp = await client!.getNewThreads(10, _pageNum);
       resp.forEach((pair) {
         var number = pair.item1;
         var msg = pair.item2;
-        items.add(ThreadItem(
+        _curItems.add(ThreadItem(
             msg.getHeaderValue("Message-Id")!,
             number,
             msg.getHeaderValue("Subject")!,
@@ -42,9 +46,18 @@ class ThreadListModel extends ChangeNotifier {
             msg.decodeTextPlainPart()!));
       });
 
-      threads[currentGroup]![pageNum] = items;
+      if (resp.isEmpty) _pageNum -= 1;
+
+      threads[currentGroup]![_pageNum] = List.from(_curItems);
     }
 
-    return items;
+    return _curItems;
+  }
+
+  void update() {
+    _curItems.clear();
+    _pageNum = -1;
+    threads[currentGroup]!.clear();
+    notifyListeners();
   }
 }

lib/thread_list_view.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import 'package:wind/thread_list_model.dart';
-import 'package:wind/thread_screen.dart';
 
 class ThreadListView extends StatefulWidget {
   @override
@@ -9,8 +8,6 @@ class ThreadListView extends StatefulWidget {
 }
 
 class ThreadListViewState extends State<ThreadListView> {
-  List<ThreadItem> _items = [];
-  int _pageNum = 0;
   String _curGroup = "";
 
   @override
@@ -24,16 +21,13 @@ class ThreadListViewState extends State<ThreadListView> {
             if (snapshot.hasData &&
                 snapshot.connectionState != ConnectionState.waiting) {
               List<ThreadItem> data = List.from(snapshot.data!);
-              _items.addAll(data);
-              if (_items.isNotEmpty &&
-                  _items.last.number != -100500 &&
-                  data.isNotEmpty)
-                _items.add(ThreadItem("", -100500, "", "", "",
+              if (data.isNotEmpty && data.last.number != -100500)
+                data.add(ThreadItem("", -100500, "", "", "",
                     "")); // magic item (for button "load more")
               return _curGroup != ""
-                  ? _threadView()
+                  ? _threadView(data)
                   : Center(
-                      child: Text("Newsgroup is not selected",
+                      child: Text("Новостная группа не выбрана",
                           style: TextStyle(
                               fontWeight: FontWeight.bold, fontSize: 16)));
             } else if (snapshot.hasError) {
@@ -46,22 +40,18 @@ class ThreadListViewState extends State<ThreadListView> {
 
   Future<List<ThreadItem>> _fetchThreadList(BuildContext context) async {
     var model = context.read<ThreadListModel>();
-    if (model.currentGroup != _curGroup) {
-      _items.clear();
     _curGroup = model.currentGroup;
-      _pageNum = 0;
-    }
-    return await model.getNewThreads(10, _pageNum, false);
+    return await model.getNewThreads(false);
   }
 
-  Widget _threadView() {
-    return _items.isNotEmpty
+  Widget _threadView(List<ThreadItem> items) {
+    return items.isNotEmpty
         ? Scrollbar(
             child: ListView.builder(
                 key: PageStorageKey("threadList"),
-                itemCount: _items.length,
+                itemCount: items.length,
                 itemBuilder: (context, index) {
-                  if (_items[index].number == -100500) {
+                  if (items[index].number == -100500) {
                     return Container(
                       height: 100,
                       padding: EdgeInsets.all(20),
@@ -72,19 +62,18 @@ class ThreadListViewState extends State<ThreadListView> {
                         ),
                         onPressed: () {
                           setState(() {
-                            _pageNum += 1;
-                            _items.removeLast();
+                            items.removeLast();
                           });
                         },
-                        child: Text('Load more'),
+                        child: Text('Загрузить больше'),
                       ),
                     );
                   } else
-                    return ThreadListItemView(item: _items[index]);
+                    return ThreadListItemView(item: items[index]);
                 }),
           )
         : Center(
-            child: Text("This newsgroup is empty",
+            child: Text("Эта новостная группа пуста",
                 style: TextStyle(fontWeight: FontWeight.bold, fontSize: 16)));
   }
 }